Summary
This meta-analysis of 106 studies reveals that nitrogen addition significantly reduces soil pH by 0.26 units on average globally, with substantial variation depending on ecosystem type, fertiliser form, and environmental factors. Grasslands show the greatest acidification, whilst boreal forests show minimal response. The analysis indicates that global soils are transitioning from a base cation buffering phase (Ca²⁺, Mg²⁺, K⁺) to an aluminium-dominated buffering phase, with implications for ecosystem health and base cation availability.
Regional applicability
The findings are globally applicable and relevant to United Kingdom conditions, where nitrogen deposition from agricultural and atmospheric sources is significant. UK grasslands, in particular, would be expected to show the acidification response patterns described, and the transition to aluminium buffering has implications for UK soil management and terrestrial ecosystem resilience. The analysis supports the need for monitoring soil pH trends in UK farming systems and grasslands subjected to elevated nitrogen inputs.
Key measures
Soil pH change (mean reduction 0.26 units globally); base cation (Ca²⁺, Mg²⁺, K⁺) and aluminium (Al³⁺) buffering capacity; responses stratified by ecosystem type, N addition rate, fertiliser form (urea, NH₄NO₃, NH₄-form), experimental duration, initial soil pH, soil carbon and nitrogen content, precipitation, and temperature
Outcomes reported
Meta-analysis of 106 studies quantifying soil pH reduction in response to nitrogen addition across ecosystem types, fertiliser forms, and environmental conditions. The study identified differential acidification responses by grassland, forest type, nitrogen fertiliser form, and experimental duration.
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